Diversity receiving system



May 23," 1944.

M. G. CROSBY DIVERSITY RECEIVING SYSITEM Filed Dec 31, 1941 4Sheets-Sheet -Z 1 '20 a J m .f-z4 54g 4T7) mm. -2E m T w 2 1 26 g g a 7=5 g5 052mm) 2 +5 (LEAMPL.

INVENTOR MURRAY 6. 02053)- ATTORNEY May 23, 1944. 1 M. G. CROSBY2,349,407

DIVERS ITY RECEIVING SYSTEM Filed Dec. 31, 1941 4 Sheets-Sheet 4 PHASEM00. LIKE UNITA MEG.

PHASE SHIFTER COMBINING AND DETECTING UNIT INVENTOR MURRAY 6. CROSBY BY7%. IWW ATTORNEY tween both the carriers and theside-barid rem; In'another. embodimentofj ny ,inv'en'tr Patented May 23, 1944 MurrayiG.CrosbmRiverhead, N. Y., assignor Radio Corporation of Delaware ofAmerica, a corporation Appucatien Decade a1, 1541, seal Ida 425,021

19'Cl'aims. (cl; 250 40) This invention relates to. a signal. receivingsystern employing a pluralityof spaced antennasfor reducing the effectsof fading. Such a receiving system is knownas adiversitysystem.-.In,such

diversity. receiving systems the phases of, the re ceived energies atthe different antennas do not remain constant but vary relatively with.fading.

The problem of overcomin'g'the variability of the ,qu hGY oscillatoryenergy which beats with one of the signals-:to produce an intermediatefre vquency. r j H r more detailed description of'the invention followsin conjunctionwith drawings, wherein Figs. -1 to 4, inclusive, showifourdifierent emphase relations between th voltages from the dif ferentreceiving antennas by automatically main- ,taining a predetermined.phase relation, so th-at the radio frequency or intermediate frequencyoltages may be combined before rectification,

has been dealt with in my UnitedStates Pat,-

ent No. 2,042,831, grantedJune 2,1936.

The presentinvention provides improvements .and refinements in themethodof. and apparatus for automatically. controlling. the re'lativev phasesof the energies from the differentantennasfof a diversity receivingsystemr MAlthough I have described in myUnited-States Patent No.2,042,831 a method of maintaining at .a constant value. the phaserelations of thecurrents received from the diversityantenna system,which includes varying the frequency of thehigh frequency oscillatorwhichv heterodynes. one fof the signals, I havefound ittobemoredesi'rable to control the phase of one of the incomingsig nalvoltages by varying a phase shifter or are? versing system. The reasonfor. thisis that when the frequency is controlled as. described' linUnited States patent supra,- instead of the" phase (in accordance withthe present invention) proper phase synchronism is not obtainedbejtweenthe higher, modulationfrequencies of the signals received over the,difierent-antennasfof the diversity system. That is,v whentheenergyreceived from thephase, detectors is. applie Ito ,thehigh frequencyoscillator in accordance with the disclosure in. my United Statespatent, p1oper phase synchronism is, obtained, for the'carrierfrequenciesbut not for the sidebandjfrequelnfcies. To obtainproperphasesynchronism be the signals received overrthediiferentantennas of the diversity system, the energy received from the:phase detectors. must be, appliedjto eife t,.a phase correction of one.of ,the'signal 'wavesl In the preferred embodiment of the invention, thereceivers functionto control 'thephase of one of the signal voltagesobtainedfrorn afr eceiver by varying a, phase shifterorfa' reversing,sys

and able. to controllthephase of one of the signal voltages by shiftingthe phase of the high frebOdirnents of the present invention. In thedrawings-{the sameparts have been labeled. by the same referencecharacters throughout the figures.

Fig l shows adiversity receiving system comprising a pair ofgeographically spaced antennas Aand A',-respectively feeding identicalheterodyne receivers I, 2; 3 and I, 2', 3'. A high frequency scillator d-fumishes beating energy; to the detectors 2 and? of the two receiversso that theintermediate frequencies obtained in inter- .mediatefrequency amplifiers, 3 and 3 are the .same.- Elementsl and. l whichcouple the antennas to the detectors 2 represent radio frequencyamplifiersn The output of intermediate frequency amplifier-3 is fedthrough line 20 directly to transformer 8 in circuit with differentialphase detectors. 5 and'6. The output of intermediatef-requency amplifier3 is fed through line 2! directly :totransformer 1 of the diflferen-.tial-detectorsi and 6.; It should be noted that thegridsofdetectors ,5and 6 receive cophasal energ-yqimpressed :on transformer l andout-ofphase lantiphasall; energy impressed on transformer 8-.., Intheoutputs of the differential phase detectors hand 6 there are; loadresistors 9 and J0, and in series relation a'pair of polar relays18,,andl9which'may be called reversing relays 011 a reversingswitch, forreasons which appear ,hereinafter 'lhe.characterof each polar relay is,such that the armature willmaintain its position iaengagementwith oneofthe contacts until such time as currentthrough the winding of therelay in the opposite direction will cause the armature to be drawn tothe oppositely disposed contact. Energy from the output of intermediatefrequency amplifier 3 is also fed through line 22 tovcouplingtransformer I 4. for applicationto the grid of the coupling tubeI I Energy from,.intermediate. frequency amplifierfi' is fed throughline 2|, not only-to the transformer l but also to the armatures ofpolar relays l8 and Ill forapplication to line 23. and transformer l3,in order that this energy can. be applied to the grid of coupling tubeI2. Transformers I, 8, l3, 'l4 and [5, are band pass tuned transformersof the conventional type, and tuned-to pass the signal frequencyrange.consisting of the carrier and side bands. It should be noted that whenthe armatures of polar relays I 8' and 19 are simul .of fading isachieved.

taneously drawn in the upward direction, the energy in line 2| isapplied to line 23 in one sense, whereas if the armatures of polarrelays I8 and I9 are simultaneously drawn in a downward direction, theenergy in line 2| is applied to line 23 in an opposite sense. In otherwords, relays I8 and I9 function as reversal relays or as a reversingswitch for reversing the direction of the current appliedironi line 2|to. line 2 3-and coupling tube 12. The energy in theoutputsof couplingtubes I I and I2 are fed to a common transformer I5 and thence to adetector and ampl ifier unit I6 to be made availableforutilization in I!which may consist of headphonesor-a loudspeaker or a suitablerecorder..-

In the operation of Fig. 1, 5 and 8 supply a voltage across resistors 9and I9, which is zero when the two carriers from the two receivers I, 2,3 and I", 2", 3' are 90 or 270 out of phase, and is of a finite valuewith a polarity depending upon the phase relation when the twocarriersjare zero or 180 out of phase. Thus, if the signal'voltages arein phase at any instant, a positive direct currentvoltage will appearacross-the resistors 9 and I0, and'if they are out of phase at anyinstant, a negative direct current voltage will appear across theseresistors; but 'if they are -90 "out of'phase, the voltage across oneresistor-opposes that across the other, so that no direct currentvoltage appears across "aphasia daatrs in both figures.

cuit composed of polar relays of Fig. 1 has been replaced by a differentform of reversing circuit composed of a vacuum tube arrangement 21 and28. In order to simplify the drawings, only that portion of the systemis shown which extends to the right of lines and 2| which arerespectively coupled to the outputs of the receivers I, 2, 3 and I, 2',3'. The antennas and receiver ele- .ments of Fig. 1 which couple tothelines 20 and 2I have not been shown in Fig. '2,=because this portion ofthe circuit is the same in the systems In Fig. 2, the energy from theoutputof receiver I, 2', 3 (applied to line 2|) is fed to transformer 39and to the coupling tube 2 6., The anode of-tube is joined to the anodessubsequent utilization in headphone, loudspeaker the combination of the.two. Putting it in-other wo'rcls, when the two signals f-rom the-receivers havea phase relation of'19 0 the direct current outputs ofthedifferenti'a-l phase detectors 5 and '6' are equal and-opposite andthere-is no change in the positionfof the armature ofthe reversingswitch comprised of polar relays-I3 and I9, 1 In this condition of 90phase difference between the two signal voltages; there is little or nodisto'rtionin: combining the-ontputs of the receivers through thecoupling'tubes I I-and I2 for utiliza;

tion in headphones I'I. However', when the incoming signals are 180apart, thecombinedenergies tend to buck-or oppose one another, and forthis reason the reversingfswitch constituting polar relays I8 fandlqjassures --th-at the outputs of the receivers are always additive." Ifit'were not for the reversingrelays-I8 and I9 operated by energy fromthe outputs of the'phase detectors 5 and 6, theocriibinede'nergieslin'theoutputs of the couplingltub les "l andI2wou1d alternately oppose (iie., buck) and aid dependingu Qn the instantaneous phase relation betweenthe energies from th two antennas/ It has: been found that this phaserelation isvery erratic and cannot be depended upon to maintain aconstant value. The desired result o f obtaining an addie e e ve vfie'ieete eas ed, A2 a never allowed to oppose or buck each otherlbutcan m ne li the eeii ef. Phas .9 re ha ese Q een ..0 ..thia he two fs il lei om e stated a t nnas are. P118? vented from J cancelling each otler and; there is obtained the full benefit of the different fadingcharacteristics of the antennas, and areduction Th systm. ofrtgfz i sdui'te similar to the sy t .of. i '1, exce t t amh re r in v ai orrecorder IT. The differential phase detectors are constituted by diodedetectors 22 and 23 instead of the triode vacuum tubes shown in Fig. 1.Diiferential energy in the outputsof'tha-diode detectors; dependent uponthe phase difference between the 'two signalsfrom the receivers;pappears across diode resistors 24 and 25 and is fed to the'suppressorgrids of reversing, tubes 2'land 2B; Vacuum tubes 21 and 2llgfunction asa reversingswitch in amanner'similar tothe' polar relays I8and I9 ofFig. 1, except-that the reversing] action is obtained in Fig. 2 bybiasing the, suppressor grid of that tube 2'! or 28 which receives ,a180 voltage on its control grid from transformer 29 so that it does notamplify, and biasing the other tube 28, or 21 receivingazero degreevoltage on its control grid from-trans former 29 so that it doesamplify,Thegrid of tube 2'I is :fed signal voltagewhich is 180 out of phase withthat fed to the grid of tube 28 from transformer 29. Consequently, thephase of .the

voltage appearing in the cornmonfianode' circuit of the two ,vacuumtubes 21 and 2.8 maybereversedby'causing one tube to be conductive; thatis 'to do the amplifying, and renderingthe other tube nonconductive. Ifthe twosignal' voltages from the receivers are out-of-phase, bothgvacuum tubes'2I and 28 furnish energy tothe and 28' differently. Atthis phase relation of 9Q, therewill be no opposing or bucking effectofthe energies combined in the detector I6. The polarity. ofthe voltagereceived by the reversing tubes 21 and 28 from the. diode resistors 24and .25 as applied to the suppressor grids, is set so that jthe propertube 21 or '28 is turned on to form an inf-phase relationbetween thevoltages from yacuum tubeifi and either vacuum tube 21 or ZQQQdependingupon which of thelast two tubes is, conducting. The combined voltagesappearing in transformer I5 are rectified and. combined in the samemanner as in Fig. 1. Transformers 29 and .30. are'band-pass tunedtransformers which are tuned topass the signal frequency rangeconsisting of the carrier and side bands. 1

Figs, 3 ,and. 4 show different systems for con tinuously maintaining thephaseof the combination ofthe signal waves at a constant value.

j, InFig.v 3 the energy from the phase detectors 5.and ,,6 is utilizedtovary the phase of one .of the signal waves in a continuous manner.,Whereas the systems of Figs. 1 and 2 merely reverse the phase of one ofthe signalwaves when, the two .voltages begin to buckv (that is,

ceivers.

oppose or cancel), the system. of: Fig. 3 maintains a' predeterminedphase relation at all times between the voltages from the two refrom thesuperheterodyne receiver I, 2',3 ',*fed over line 2|, is applied to theinput terminals of an artificial line 32 which is terminated by a surgeimpedance or resistor R equal in value to the surge impedance orresistance of the line 32. By virtue of the, termination of line 32 atthedesired intermediate frequency, only traveling waves appear in theinductive portion of the line. A pair of electron'discharge devicemodulators 33 and 34 have their control electrodes tapped throughblocking condensers C, C

to points P and P on the inductance coil of the line 32, which pointssupply voltages to the control; grids approximately 90? apart.Accordingly, voltages of the same or like frequency that supplied fromline 2! are fed to the control grids of the modulator tubes 33 and 34ninety degrees apart.v The anode circuits of both modulator tubesarejoined together and to a tuned circuit forming part of the transformerTR. Transformer TR is a band-pass tuned transformer which is tuned topass the signal frequency range consisting of the carrier and sidebands.In accordance with the invention, it is proposed tooppositely vary theoutput of the modulator tubes 33 and 34 in order to vary the phase ofthe resultant voltage from the two tubes between two limits. I'Ihisshift in phase of the 'resultant cons tituting the' output of themodulator tubes 33 v,and 34 is"accompl ished by relatively decreasingthe amplified voltage appearing in theoutpllt of one of themodulatorrtubes 33 or 34 and relatively increasing the amplified voltagefrom the other. modulator tube 34 or 33 appearingin the output circuit.In order to cause thisopposite variation inputput voltagefinmodulator.tubes 33 andv 3 the anode circuits .of the phase detectors 5 and 6 areconnected to the screen grids of the modulator tubes to apply tothesescreen grids the difierential voltage from the phase detectors. It willi the phase of the energy in the common anode circuit of the twomodulator tubes will change.

The phase shifter 32 and the modulator tubes 33 and with their commonoutput'circuithave been indicated in dotted lines andlabeled as unit A;Thisunitis identical in construction with the apparatus-in units B andC, all of which, it should be noted-areconnected together to the sameleads extending to theresistors 9 and I in the outputs of the phasedetectors and 6. The same process previously-described as taking placeinunit A will simultaneously take place in units-B and C which-arecascaded with unit A so as to produce a-greater phase variation than isobtainable in only one of the'units. This greater phase variation occursbecause all the phase changes in units A,-B"and C addup together toproduce a resultant which is fed via When the phase relation between Theintermediate frequency energy .line 42 to the combining circuit 35,after which the energies are fed to. detector and audio frequencyamplifier l6 for utilization in head- 'phones, loudspeaker or recorderI'I. Combining circuit 35 may comprise coupling tubes such as H and11l2of Fig. 1. By using proper connections with a suitable adjustment of thepolarities, the energy from the phase detectors 5 and 6 will cause phasemodulator units A, B and C toapply a" phase correction to the energyfrom line 2!, sofltha'tthe voltages fed to detectors 5 iand i viatransformers 8 and I will be brought 'back'to'the desired relation. Inthis way the voltages fed to the phase detectors will be continuously i"maintained at or near the 90 desired phaser'elation position. The energyfrom receiver l, 2 and 3 and line 20 is fed to a suitable phase shifter36, in order that it may be combined by apparatus 35 with the energyfrom line 42, the last energy being obtained fromreceiver I, 2', 3', andline 2L. Phase, shifter 36 may take the form of the artificial line typeof phase shifter 32, orany other suitable. form such as that describedin my United States Patent No. 2,247,9e1. Apparatus 35 constitutessuitable vacuum tube apparatus for combining energies in known manner.The combined energy is thendet'ectedin' unit l6 and made availableforjutilization. v V

",1" One advantage of the system of Fig. 3 over known methods ofmaintaining continuous control of the phase relation between thevoltages from. the two receivers is that I employ electronic controlwhereas'I previously described (in my." United :States Patent No,2,042,831, Fig. 1 thereof) a motor control arrangement. Theelectroniccontro1 scheme of the present invention is much faster inoperation'than the motor control method of] accomplishing a.,similarresult. a

The system ofFig. 4 obtains a continuous and automatic icontrolof thephase relations between theoutputsof the two superheterodyne receiversofthe diversity system by shifting the phase of the high frequencyoscillator energy instead 'of thatin the intermediate frequency energyas shown inFigs. 1, 2 and 3. In Fig. 4, the energy from the highfrequency heterodyne oscillator 4 is phase. modulated at a relativelylow frequency by modulator unit 31, which is like apparatus A of'Fig. 3.More specifically, unit 31 is a phase modulator employing two vacuumtubes and a phase shifter of the type shown in Fig. 3. This phasemodulator 31 is controlled from the out- 'put of differential phasedetectors 5 and 6 in the 's'ameimanner as described hereinabove inconnection' with Fig. 3. The output of the phase modulator ,3? isfrequency multiplied by frequency multiplier unit 38 so as to increasethe degree of phase modulation effected by unit 31. A similar frequencymultiplier 38 is located in th'e'i'ine feeding high frequency oscillatorenergy unit; to the detector 2 of receiver I, 2', 3'. the'operatio'n ofthe. system of Fig. 4, the 'differe'ntiallydetected output from 5 and 6is fed to the phase modulator unit, 3,! so as to correct the phase ofthe high frequency oscillator energy fed thereto by unit 14, and in'turncorrect the phase relation between the two signal waves inthe-two'receive'rs so as to maintain a 90 phase relationbetween theenergizes from the two antennasAand A; These two energies with constantphaserelation are then fedto combining and d'etectingfunits 39, oneofthem being phase shifted to the desired-relationship-by meansof phaseshifter, 36.. The couplingtubes of unit 39 arethel same ascouplingftubes 'H and 'l2 of Fig. 1. @Instead of showing '(in Fig. 4)'theusual ldetecto'rs l6 and I] as illustrated in Figs. 1, 2 and 3, Ishow a' j ack 40 toindicate-that any suitablefutilization'circuit maybelinked there to. This feature, may also be used in any one 'ofthejs'y'stem's of the other'figure's of thedrawings.

In the diversity, receiving system. of Fig. 4, the phase modulatorunitcan be arranged, if desired, to correct the phase of the secondintermediate frequency oscillator in a triple detection superheterodynereceiver, instead ofthe high frequency oscillator as isshown'. Bycorrecting the second oscillator, there'is obtained the advantage of anincrease in the flexibility of the receiver, since the phase modulatorand the frequency multipliers would not' then have to be tuned to tunein different "signals.

. Although thefdrawings show only two antennas in a diversity system, itwill be understood that the circuits are not limited to two antennas andthat if desired "a third a'ntennawithan associated third receiver canalso be used. If such a third antenna is employed, the collected energyfrom the third antenna can be combined with the collected energy fromthe'first two antennas by considering the combined outputof the firsttwo antennas asa single output 'and'th'en 'combining, the energy'fromthe third antenna with the combination of'the first two. This is a typeof family tree arrangement which can be extended to combine the energiesfrom any number of antennas ina deliversity receiving, system. Anothermethod of combining the energies collected from more than two antennaswould be to consider one of the receivers associated with an antenna asvthe standard to which the receivers of the other two antennas are to becombined; thus, such an arrangement would make twoof the antennas inphase with the third one, so. that they would be in phase with eachother. What isclaimed'is:

1. The method of operating a diversity receiving system which includescollecting signal energyat two spaced points, combining the energiescollected, producing a single voltage responsive to relativevariations'in phase of the two collected energies and utilizing saidvoltage to produce fixed changes of 180. in the phase relation of thecombined energies.

2.. Aradio receiving system comprising a pair of antennas, adifferential detectonmeans for feeding energy collected upon one antennacophasallyto said detector, means for feeding energy collected upon theother antenna antiphasally to said detector, an energycombining circuit,separate paths coupling each of said antennas tosaid energy combiningcircuit, and means responsive to an unbalance in the output of saiddifferential detector for reversing the connections of one of the pathsto said combining circuit, whereby the polarity of the energy .in saidone path applied to said combining circuit is also reversed. h

3. A' radio receiving system comprising .apair of spaced antennas, areceiverfor each of said antennas including an oscillator in common tosaid receivers for heterodyning with the waves collected by saidantennas to produce an intermediate frequency, a differential phasedetector comprising a pair of vacuum tubes, a connection between thecathodes of said vacuum .tubes, a

first transformer having a pair of tuned circuits anew one of which isconnected betweenlikeelectrodes of said vacuum tubes for applyingout-of-phasc 'potentialsthereto and the other of which is connected tothe intermediate frequency output of one receiver, a second transformerhaving a pair of tuned circuits one of which is connectedbetween thecathodes of said vacuum tube and the electrical center of said one tunedcircuit, of said first transformer for applying iii-phase potentials tosaid like electrodesand .the other circuit of whichis connected to theintermediate frequency output of the other receiver, an energy combiningcircuit, separate paths from the intermediate frequency outputs ofsaidreceivers to -said energy combining circuit, each of said pathsincluding a coupling vacuum tube, and. a circuit coupled to saiddifferential phase/detector and responsive to an unbalance in the outputof said detector for reversing the connections of one .of said paths. H

4. A radio receiving system comprisinga pair of spaced antennas, areceiver for each ofsaid antennas, a differentialphase'detectoncomprising a pair of vacuumtubes, aconnection between thecathodes of said vacuum tubes, a first transformer having a pair oftuned-circuits one. of which is connected between like electrodes ofsaid vacuum tubes for applying'outeofephasepotentials thereto and theother tuned circuitof which is connected to one receiver, a secondtransformer having a pair of coils one of which is connected between thecathodes of said vacuum tubes and the electricalcenter .of the-firsttuned circuit of said first transformer forapplying in-phase potentialsto said like electrodes and the other tuned circuit of which isconnected to the other receiver, anenergy combining circuit, separatepaths from said receivers to said energy, combining circuit, each ofsaid paths including'a coupling vacuum tube, and a. circuit coupled tosaid differential phase detector and responsive to an unbalance in theoutput of said detector for reversing the connections of oneof saidpaths. I

5. A system in accordance with. claim 6, characterlzed in this that saidcircuit coupled to the differential phase detector and responsive .toanunbalance in the output of the. detector for reversing the connectionsof one of-the paths includes a pair of polar relays whose windings arein series and connected to like electrodes of the detector, said onepath including'thearmatures of said polar relay and certain contactsthereof.

6. A system in accordance with.,claim 4, characterized in this that saidcircuit coupled to the difierential phase detectorand responsive to anunbalance in the output of thedetector for reversing thepolarity of oneof the paths includes a multi-grid tube whose suppressor grid isconnected to the detector circuit and-whose-control grid is coupled tosaid one path.

7. A radio receiving system comprising a pair of antennas, likereceivers for said antennas, a differential phase detector comprising apair of vacuum tubes, a circuit from one receiver to said detector tofeed energy in out-of-phase relation to said vacuum tubes, a circuitfrom the other receiver to said detector to feed energy in cophasalrelation to said vacuum tubes, whereby no differential voltage appearsinthe output of said detector when the signal waves from the tworeceivers applied to said detector are out-ofphase, an energy combiningcircuit, separate paths from said receivers to said energy combiningcircuit to apply high frequency energy therem et to, and a polarityreversing circuit located in one of said paths, said reversing circuitbeing coupled to said phase detector'and'jresponsiveto an unbalance inthoutput of said detector caused'by adeparture of the signal waves fromsaid 90' relation for reversing thelconnections of said one path. I i v,I v V 8. Ina radio receiv'ing system, a pair of antennas,like'receiversffor said antennas,a"difsaid vacuum tubes, aicircuit fromthe other receiverto saiddetectorj tofeed energy in cophasal relation tosaid' vacuumjtubes; whereby no dif ferential voltage appears in theout'put of i said detector when the'signaljwave 'ir'om said two receivers applied tosaid' de'tectoi' are 90 ,outjof-" phasaj one of "saidcircuits including a pair'or thermionic discharge devices ea'ch havinganode, j cathode, control grid and screen "gridielectrodes, there beingprovidedineans for feeding' theen-I ergy in said one 'circuitt'o saidcontrol grids 90, out-offipha'se relative to each other, a direct con-'nection' between the fi pdes" of said devices I for combining "the"outputs of said devices to obtain resultant energyoi likeirequency astheirequency of the waves "in* said one circuit, connections from theoutput of said differential phase detector for applying potentials inphase opposition to said screen grids whenever there is an unbalance inthe output of said phase detector, an energy combining circuit, a pathfrom one receiver to said energy combining circuit, said path includinga phase shifter, a path from the outputs of said thermionic devices tosaid energy combining circuit, and translating means coupled to theoutput of said energy combining circuit.

9. In a radio receiving system, a pair of an tennas, like receivers forsaid antennas, a differential phase detector comprising a pair of vacuumtubes, a circuit from one receiver to said detector to feed energy inout-of-phase relation to said vacuum tubes, a circuit from the otherreceiver to said detector to feed energy in cophasal relation to saidvacuum tubes, whereby no differential voltage appears in the output ofsaid detector when the signal waves from said two receivers applied tosaid detector are 90 out-of-phase, one of said circuits including a pairof thermionic discharge devices, each having a plurality of electrodes,a transmission line having its input terminals connected to the receiverassociated with said one circuit and its output terminals terminated byan impedance of such a value as to cause only traveling waves to appearin said line, connections between points. on said line which are 90apart to the control electrodes of said devices, a direct connectionbetween the output electrodes of said devices, connections from theoutput of said differential phase detector for applying potentials inphase opposition to other like electrodes of said devices whenever thereis an unbalance in the output of said phase detector, an energycombining circuit, a path from one receiver to said energy combiningcircuit, said path including a phase shifter, a path from the outputs ofsaid thermionic devices to said energy combining circuit, andtranslating means coupled to the output of said energy combiningcircuit.

10. Apparatus for reducing the fading of received radio waves comprisinga pair of antennas for collecting transmitted waves, a differentialdetector, means for feeding energies collected upon one antennacophasallyto the difierential detector, means for ,feeding' energiescollected upon the otherj'antenn'a antiphasally to saidjdiiferentialdetector, purely .electronicmeans for' maintaining a predetermined phasedisplacement between the energies respectively fed to said'diL ferentialdetector, the last said'mean's beingre sponsive to an unbalancing of theoutput from said detector, and means for translating'and 'uti flizing'ithe outputs of said antennas. i V

11; Apparatu for receiving radio waves com prisingfpair'of antennae, areceiver for each antenna, a d ifier'ential detector, means for feed ingenergy from onereceiver-cophasally to said" differential detector, meansfor feeding energy from the other receiveriantiphasally .to, said 'dif-Ifer e'ntial detector, meansincluding a difierential modulator coupledbetween the output of. said detector and theoutput of one receiver formain taining a predetermined phase displacement. between the energiesfed to, said differential detector, and means ffo'r combining andtranslating the outputs of said'rec'eive'rs.

12 A receiving, system comprising .a vpair 1of antennas, a receiver for,each antenna, ajlocal heterodyne oscillator having a connection t'oIonereceiver and a' connection to the other receiver for ca using theenergies collected. by said antenn'as' andimpr'essed on said receivers'to'be converted to an intermediate frequency, a phase modulator in oneof said connections for shifting the phase of the oscillator energytherein, a dilferential phase detector, a circuit from one receiver forfeeding intermediate frequency energy cophasally to said detector, acircuit from -the other receiver for feeding intermediate frequencyenergy antiphasally to said detector, and a circuit from the output ofsaid detector to said phase modulator, whereby an unbalance in theoutputs of said detector affects said phase modulator to correct thephase of the oscillator energy supplied to one of the receivers tothereby correct the phase relation between the energies supplied to saiddetector to maintain a substantially phase relation therebetween.

13. A receiving system comprising a pair of antennas, a receiver foreach antenna, a local heterodyne oscillator having a connection to onereceiver and a connection to the other receiver for causing the energiescollected by said antennas and impressed on said receivers to beconverted to an intermediate frequency, a phase modulator in one of saidconnections for shifting the phase of the oscillator energy therein, adifferential phase detector, a circuit from one receiver for feedingintermediate frequency energy cophasally to said detector, a circuitfrom the other receiver for feeding intermediate frequen cy energyantiphasally to said detector, and a circuit from the output of saiddetector to said phase modulator, whereby an unbalance in the output ofsaid detector afiects said phase modulator to correct the phase of theoscillator energy supplied to one of the receivers to thereby correctthe phase relation between the energies supplied to said detector tomaintain a substantially 90 phase relation therebetween, and separatemeans for combining and detecting the outputs of said receivers.

14. A receiving system in; accordance with claim 13, including afrequency multiplier connected to the output of said phase modulator inorder to increase the degree of phase modulation afiected by saidmodulator.

15. A receiving system in accordance with clai nilli eani g a friiniicynrultipliericon-f nected to the output of ,sa d pliasemodulatorinorderito increase the degree of phasellnodulation f c b a d at tenda soin v i eia like-frequency multiplier in the other connection from thelocal oscillator to the other receiver.

16.. The method of operatinga dive'rsli t y ire:

ceiying" system, which includes collectingjsignal energy at twospaced'poin'ts; detecting in one= circuit a part oi the signal encrgiesjhlis collected, diverting to another' circuitthe remaining r Qi' e eneres ime qll eq d P o n -f voltagewhose'polarity'changes in response torelative variations injthe phaseoflthe energies detected in'saidonejcircuim. and utilizingsaid voltage to produce ,a relative change inthe phasefofthe signal energies diverted to said other circuit. f

17. The method of reducing jfad l Qradio:

signals which includes collecting the signal, ,en}

ergy' at two spaced points,' cornbinin'g the 'co1 lected energies;producinglasingl e voltage ire sponsive to relative variations in phaseof the two collected energiesjand. utilizing said voltage to' producefixed changes I of predetermined am'ountin the phase relation of thecombined ie v4 18. A radio receiving system comprising a pair than? orass sts; a mama"mama; mefani s for feeding energy; collected, upon .oneantennaucor phasally to said detector, meansv for .feeding en.-.- ergycollected upon the, other antenna, anti-0. phasally to said detector, anenergycombiningx circuit, separate paths coupling each .ofmsaidoantennas to said ener y combinin circuit,-and

means responsive to an ,unbalancein the output of said difierentialdetector for changinathe relative phase of the energies in said separatepaths.

19. Apparatus :for reducing the fading fof reel.

ceiyed radio waves comprising a pair ,of an:

tennas Ior collecting transmitted waves, a. :dif;

ferential detector means Y for feeding energies collecteduponhoneuantenna cophasally tohthe.

antennas. a.

MURRAY G. CROSBY.

